core: remove parent_id from the global event

Remove the parent_id from the global event. Remove the parent
and owner from the global object.

Use properties instead to mark parents and owners of objects.

Properties are easier to control for client exported objects and
usually a simple parent/child is not enough. For example, a client
exported node has the client as a parent but also the factory that
created the node.

src/tests/test-interfaces.c

@@ -106,7 +106,7 @@ static void test_registry_abi(void)
 	} methods = { PW_VERSION_REGISTRY_PROXY_METHODS, };
 	struct {
 		uint32_t version;
-		void (*global) (void *object, uint32_t id, uint32_t parent_id,
+		void (*global) (void *object, uint32_t id,
 			uint32_t permissions, uint32_t type, uint32_t version,
 			const struct spa_dict *props);
 		void (*global_remove) (void *object, uint32_t id);